An example of preparation of a sample consists of extracting and subsequently purifying biological material for use in subsequent analysis. Preparation of the biologic sample, including extraction of DNA and subsequent purification, also referred to as “sample preparation”, is the starting point of numerous processes of DNA analysis, such as RT-PCR, electrophoresis, genotyping, etc.
Currently, sample preparation can be performed using suitable kits available on the market, which are operated manually performing a particular procedure. FIG. 1 illustrates the so-called “spin-column method” that is among the most widely used sample-preparation procedures. With reference to FIG. 1, the process implemented by this method includes four steps.
In a first step, referred to as “pretreatment”, the selected biologic sample, from which the DNA is to be extracted, for example whole blood, is subjected to a cell lysis comprising dissolving the cell by disrupting the cell membrane. Lysis is carried out, e.g., by arranging the biologic sample in a hypotonic solution. After lysis, using suitable enzymes such as proteinase K, digestion of the contaminating proteins is performed.
The second step, referred to as “DNA binding”, consists of the separation and recovery of the nucleic acid from the solution containing the lysed cell material. One of the most recent methods consists in the use of a matrix of silica gel in presence of chaotropic salts that adsorbs and binds the DNA.
In the third step, referred to as “washing”, the gel matrix is washed using a suitable solution such as, for example, buffer and/or ethanol, in order to eliminate interfering residue, such as proteins and lipids.
In the fourth step, referred to as “elution”, the silica-gel matrix, binding the DNA, is eluted using an aqueous solution with low saline concentration. By virtue of this treatment, the DNA previously captured on the surface of the gel matrix is removed and made available in a solution within the test tube. The prepared sample is ready for use in the downstream application, for example RT-PCR.
In order to carry out RT-PCR, the prepared sample is subsequently collected with a pipette and transferred into the wells provided in a silicon chip accommodated on a disposable cartridge. Next, this cartridge is inserted in a thermal cycler with a fluorescence detector for carrying out DNA analysis.
All of the previously described steps regarding preparation of the sample and loading of the prepared sample into the wells in a silicon chip are performed manually using the devices provided with the kit (test tubes, pipettes, buffers, etc.). The sequence of the various steps involves handling a large number of devices and transferring liquids in the transition from one step to the next of the method.
Because of the large number of manoeuvres and devices involved and the precision required in the manual manipulations, the method is particularly slow, cumbersome in its implementation, and exposed to accidental errors of execution and to contamination by the surrounding environment. Thereby it is, as a whole, far from robust and reliable in relation to the quality of the end result.
The method described above is moreover far from effective in terms of economic yield, requiring the use of large amounts of costly reagents. Finally, it can be carried out only by highly specialized staff, limiting use thereof to just the hospital and/or laboratory environment.